The present invention is related to driving fasteners into hardened structures such as concrete ceilings and floors, concrete columns and structural steel members such as I-beams. When such fasteners are to be driven, the working quarters are sometimes cramped with existing structures and equipment. This may result in awkward or limited access to the sites to which the fasteners are to be mounted. This is especially the case with ceilings, which frequently require the use of poles to hold the driving tool in place. Compounding these circumstances is the frequent requirement that a large number of fasteners be mounted, as in the case of suspended ceilings, as known in the art. Thus, efforts have been undertaken to improve worker productivity, while not sacrificing safety. Fasteners have been driven into such structures using various explosive, detonatable, ignitable or combustible charges.
Various types of systems have been used in the prior art. Such systems are characterized as low velocity (discharging a fastener at less than approximately 300 feet/second), medium velocity (discharging a fastener at a velocity of 300-500 feet/second), high velocity (discharging a fastener at a velocity of greater than 500 feet/second), and zero stand-off systems. All but the zero stand-off systems are characterized as being ballistic in nature, because the fasteners can attain free flight. Such systems have safety concerns analogous to handling firearms, but have found application in imbedding fasteners in particularly hard structures in which considerable penetration depths of the fasteners are desired.
The zero stand off-type systems do not achieve free flight of the fasteners. These systems have reduced similarities to firearms, but often at the expense of sufficient power to achieve the desired holding penetration in the target structure. A common characteristic of this second type of system is to use the presence of the target structure or work surface asa necessary prerequisite to actuating the firing of the power charge. This is typically achieved by providing a barrel structure having a bore therein for holding a power charge or cartridge and a fastener. The fastener extends out of the barrel and into contact with the work surface. When the barrel is driven toward the work surface, the fastener is driven inwardly toward the cartridge and serves as a firing pin for detonating or igniting the charge in the cartridge. This results in the compressed ignition gases resulting from the ignited power charge forcing the fastener out of the barrel and into the work surface of the target structure. Hence, as a result of the cooperation of the work surface, barrel, power charge and fastener, with the fastener functioning as a firing pin, a relatively safe, non-ballistic or non-free flight system is provided. Unfortunately, in the prior art systems, the power achieved and hence the degree of penetration of the fastener into the target structure are limited.
Exemplary of such zero stand-off tools for driving explosive-actuated or self-energized fasteners is the tool of U.S. Pat. No. 3,797,721 to Clumb. That patent discloses a tool having a barrel with a bore for positioning the fastener to be driven. The bore is stepped with a shoulder at the muzzle for supporting a guide washer friction-fitted to and slidable along the fastener. A second shoulder is provided for supporting the rim of an explosive charge cartridge. The portion of the bore beneath the second shoulder defines an explosive chamber. A closed gas expansion chamber surrounds the barrel and communicates with the bore through a plurality of outwardly opening frusto-conical passageways. In operation, the explosive charge cartridge is loaded into the bore. The fastener is then placed in the muzzle of the bore. By placing the pointed end of the fastener against the work surface and either striking the end of the tool or striking the fastener against the work surface, the fastener slides along the bore against the explosive charge cartridge, thereby serving as a firing pin and detonating the charge and forcing the fastener into the work surface.
Similarly, U.S. Pat. No. 3,172,123 to Helderman et al. discloses a system in which a spring-loaded barrel is forced toward the work surface, thereby forcing the fastener inwardly into the bore of the barrel to act as a firing pin for igniting a power charge disposed at the head end of the fastener.
A self-energizing fastener system is disclosed in U.S. Pat. No. 4,899,919 to Clumb. That patent also discloses a tool in which the fastener is to be forced against a protrusion inside the barrel of the tool with the fastener serving as a firing pin in order to ignite the power charge. The fastener includes a pellet propellant charge which is affixed to the head of the fastener. A similar fastener is shown in U.S. Pat. No. 3,559,272 to Hsu, in which a power pill is attached to the head of a drive pin.
Materials used for power charges have included nitrocellulose in various forms. Exemplary of such power charges are those disclosed in Clumb '919 and Hsu '272, as well as in multistage power loads disclosed in U.S. Pat. No. 3,648,616 to Hsu and in caseless cartridges disclosed in U.S. Pat. No. 3,398,684 to Kvavle.
Mounting of a suspension clip to a fastener is also addressed in the prior art. U.S. Pat. Nos. 3,665,583 and 3,805,472 to Helderman are each directed to a fastener and suspension clip structure which includes a retaining flange for facilitating the holding of the suspension clip on a power actuated tool so that the clip can be fastened to a ceiling by a fastener stud to be driven by the tool. The clip is flattened to conform to the barrel muzzle, with a hole provided to accommodate the fastener stud. A tool, similar to that disclosed in the Clumb '721 patent, is also described.